1. Field of the Invention
This invention relates to a method of fabricating an optical package for use in an optical transmission system.
2. Prior Art
In the field of optoelectronics, optical packages have been the subject of much study, especially methods of precisely attaching and aligning an optical fiber to a semiconductor laser or other active optical components. Coupling between an optical fiber and a semiconductor laser requires a high degree of care in fabrication, particularly when an optical package is designed for a high frequency, single mode transmission system. Direct attachment of an optical fiber to a semiconductor laser can be disrupted when the operating temperature of the semiconductor laser fluctuates and causes different dimensional changes respectively in the optical fiber and the semiconductor laser. The dimensional changes in response to temperature fluctuation cause the optical fiber to become separated from the semiconductor laser. In addition, direct coupling is generally inefficient because of a wide disparity in the dimensions of the guided modes in the semiconductor laser and the optical fiber. This can be overcome by the use of a lens for mode size matching.
A copending U.S. patent application Ser. No. 546,381 (now U.S. Pat. No. 5,073,047) discloses an optical package or module designed for a high frequency, single mode transmission system. The optical package generally comprises a housing, a laser holder by which a semiconductor laser is held, and a fiber holder including a ferrule by which an optical fiber is held. The housing is composed of two sections welded together. A first section of the housing has a rod lens for focusing optical emission from the semiconductor laser on the optical fiber. The other section of the housing has a bore to receive the ferrule. The laser holder and the fiber holder are attached to the first and second sections of the housing, respectively. It should be understood that when the laser assembly is fit in the laser holder, the optical axis of a semiconductor element or chip may not precisely be aligned with the central axis of the laser holder. This is due to the fact that such a semiconductor chip is occasionally not precisely positioned as it should be, because, mainly, of manufacturing tolerance. In the case that the optical axis of the semiconductor chip is offset from the central axis of the laser holder after it has been assembled to the laser holder, then such an offset increases under the influence of the rod lens. Accordingly, the second section of the housing is moved in a radial direction relative to the optical axis of the laser until maximum optical output is attained. However, this adjustment is often time-consuming.